Electronics Forum

Electronics Circuits & Projects discussion forum. Get help with electronics.


Q point for a BJT

Discuss all your electronics engineering related technical problems and other questions pertaining to design problems in any field of Electrical/Electronics/Computer Hardware

Moderator: pebe

Q point for a BJT

Postby didi10 » Tue Dec 04, 2012 4:16 pm

I need a relationship (equation) between Cpi and the Q point for a BJT.
didi10
 
Posts: 2
Joined: Tue Dec 04, 2012 3:54 pm

Re: Q point for a BJT

Postby sachinelectrostar » Fri Oct 11, 2013 9:16 am

Vbe - Vcc + (Ic + Ib)Rc + IbRb = 0

sinc Ic >> Ib we can simplify to

Vbe - Vcc + IcRc + IbRb = 0

because Ib = Ic/beta we can solve for Ic to get

Ic = (Vcc - Vbe) / (Rc + Rb/beta)
sachinelectrostar
 
Posts: 8
Joined: Wed Sep 25, 2013 7:38 am
Location: Noida

Re: Q point for a BJT

Postby dscpcb » Fri Sep 11, 2015 12:38 pm

The Q, or quiescent point, is the DC level, or where the circuit produces no noise.
The first thing to do would be to Thevenize the left side of the circuit; Vth = 24K/(24K+96K) * Vcc, Rth = 96K in parallel with 24K.

Once you solve those, you will have a circuit with an a voltage source on the left (Vth) and a resistor, Rth, between Vth and Vbe.

To solve for the current i(b), use i(b) = (Vth - Vbe)/Rth

Once you have i(b), you should be able to find i(c) and Vce, and then verify that the circuit is in active mode.
dscpcb
 
Posts: 4
Joined: Fri Sep 11, 2015 12:13 pm

Re: Q point for a BJT

Postby bwetman » Mon Dec 28, 2015 12:42 pm

Hello,
The operating point of a BJT, also known as bias point or quiescent point (or simply Q-point), is the DC voltage and/or current which, when applied to a device, causes it to operate in a certain desired fashion.
PCB Repair Tools - Rework Stencils, & SMT Stencils on Soldertools
bwetman
 
Posts: 15
Joined: Mon May 11, 2015 7:00 am
Location: Rolling Meadows, IL 60008


Return to EE quiz questions & problems



Who is online

Users browsing this forum: No registered users and 1 guest

1PC NEW SMC SS5Y5-20-05 Solenoid valve base manifold #YP1
$60.0
1PC NEW SMC SS5Y5-20-05 Solenoid valve base manifold  #YP1 pictureONE BRAND NEW SMC VQ110U-5L-M5 Solenoid Valve #YP1
$40.0
ONE BRAND NEW SMC VQ110U-5L-M5 Solenoid Valve  #YP1 picture1PCS NEW FOR SMC VQ110-5M Solenoid valve head #YP1
$46.0
1PCS NEW FOR SMC VQ110-5M Solenoid valve head  #YP1 picture12V Plastic Magnetic N/C Normally Closed Quick Insert Inlet Water Solenoid Valve
$4.9
12V Plastic Magnetic N/C Normally Closed Quick Insert Inlet Water Solenoid Valve picture


cron